In MS Physics, is it possible to maintain and object inside a rotating cylinder? If I make the cylinder a static mesh it will not rotate. If I don't make the cylinder a static mesh, the object will go through the walls. Please see attached SU 2015 animation.

To fix this, you have to divide the concave cylinder group into sub convex groups, so that the hollow cylinder is made up of additional internal groups. This can be done with Convexify plugin, by fredo6, which automatically divides solid concave shapes into convex groups. Then the top level shape must be set to compound.

For your model, before using convexity, first divide the outer, hollow cylinder and the inner mixer into separate, internal groups. Then, set the outer cylinder's state to Ignore. You won't need it part of simulation because the green cells will serve as the collision instead. Then ensure that the mixer part is solid (has a valid volume) and doesn't have any invalid geometry. You can use TT Solid Inspector and TT Cleanup for that. Ensuring that the mixer is solid, will yield the proper generation of convex sub-groups when you use the Convexify.

The fixed versions of your model is attached below. You can also try fixing it yourself, by following the instructions above, so that you know how it's done. Also, next time, use components for the green cells to reduce file size.

Well, since you removed the cells, that initially served as a collision, you will have to apply Convexify to the outer, hollow cylinder. When you do so, ensure that convexified parts are inside the group where the convexified mixer is and that they are not ignored. You can check out the videos at Convexify's homepage for instructions on how to use it.